DE2331591B2 - Procedure for the transmission of underwater signals - Google Patents

Description

F i g. Figure 3 illustrates a scheme showing multiple propagation paths under water and between a transmitter on the one hand near the surface and a Receiver on the other hand shows at the bottom of the sea,

J i g. 4 the time-dependent changes in the carrier frequency shows when sending and receiving,

F i g. 5 shows a voltage / frequency converter, in the in F i g. I used the transmitter shown and

F i g. 6 that shown in FIG. 1 in more detail Receiver shows.

F i g. 1 shows a transmitter 1 which receives the information signals to be transmitted on a terminal 2 and which transmits ultrasonic frequency signals to a transducer 3, the task of which is therein. Transmitting ultrasonic waves into a liquid medium represented by arrow 4; further a receiver 5 using an ultrasonic wave transducer 6 is equipped to receive the ultrasonic waves emitted by 3, after which the rectified Signals from an output terminal 7 for information signals are transmitted.

In accordance with the system according to the invention the transmitter 1 an oscillator 8, the frequency of which you !; changes according to a linear law and df.'ii a modulator 9 and a power amplifier 10 tut 'is switched. whose output to the converter 3 vci. andes is. The transferred to terminal 2 In: irmationssignale are processed in a circuit 11, which is, for example, a Analog / digital converter can act, which converts the analog information transmitted to terminal 2 into converts a coded pulse train, which is then transmitted to the modulator 9. Furthermore a clock generator 12 is provided with the purpose of synchronizing the oscillator 8 and the operation of the To ensure converter 11.

The receiver 5 comprises an analog multiplier 13, one input of which is connected to the converter 6 connected and followed by a bandpass filter (filter 14), which in turn is followed by a demodulator rectifier 15. The second input of the multiplier 13 is connected to the output of a local oscillator 16, the frequency of which is the same linear relationship like that of the oscillator 8 changes.

In the transmitter 1, a synchronization signal generator 17 transmits synchronization signals to the amplifier 10, which are filtered out in the receiver 5 in a filter 18, which is followed by a logic circuit 19 which transmits the synchronization signals to the local oscillator 16 in such a way that its frequency change with that of the oscillator 8 is synchronized. The generator 17 is also connected to the clock generator 12. Before the mode of operation of the circuits of the transmitter 1 and of the receiver 5 is described in detail, as shown in FIG. 5 describes the case of a transmission that takes place between the transmitter 1 and the receiver 5 at a certain horizontal distance r and a depth h , the value for "r" being significantly greater than the value for "/ i" (the transmitter 1 is assumed to be on the surface of the sea, the receiver 5 on the bottom). Under these conditions, between 1 and 5, several transmission or propagation routes are possible.

When receiving it by the receiver 5, the angle results! θο the direct propagation distance through the relationship:

Ma = arc tg

H'

This also results for the angle of incidence Ho of the η-th interference propagation path (in Fig. 3 η = 2):

π = arc tg ~ Ρ) ~~ τ ~ ϊττΓ ■

The length of the optical path of the direct path of propagation is given by the following relationship:

h zo =

cos Ho

This also results for the nth disturbance propagation path:

(2 ii + Vi H

zn = .

cos Wn

as The energy loss (without taking into account the Absorption) results from the well-known relationship:

H = 20 log zn + ti R ,

where II in dB. _ / i can be expressed in meters and R as a coefficient that depends on the angle of incidence and on the nature of the elements that make up the seabed.

Thus, for example, for r = 2000 m and /; = 80 m the following table of values:

87 '71 0 length 1 Ver running time Slrek- 83Ί5 0 in m losses i.i ms ke 78 "69 0.46 2002.1 66 1334.75 0 74 35 1.3 2014.34 66 1342.89 1 70 20 1.5 2039.6 67.2 1359.73 2 2076.9 69.9 1384.61 3 2125.56 72 1417.10 4th

delay

8.1
25th
49.8
82,352

This table shows. that under the condition To be able to neglect routes, the level of which is at least 3 dB attenuated, beyond that there are still three propagation paths left that must be taken into account. It should also be noted that that the third propagation stretch has a delay of 25 ms compared to the first.

It could easily be demonstrated that a simple amplitude modulation leads to a reception that would be disturbed by recombinations of signals from different propagation paths would be or at least make the modulation more difficult, which would be made by a sufficiently redundant pulse coding of the type of error-corrected code is transmitted. In addition, confused without further ado recognize that the coherence of a conventional frequency modulation is destroyed by the recombinations would.

The representation of the F i g. 4 leaves the operating mode of the transmission system according to the invention in a simple manner recognize.

The in I'i g. The curve 20 shown in FIG. 4 represents the change in the frequency of the carrier at the output of the circuit 8 of the transmitter I as a function of the / eil t. ie. that in each frequency cycle the frequency rises linearly from FO to FS : then this is fed very quickly to the Irequen / FO and remains constant and equal to the value FO for a short time interval. The frequency change cycle is then resumed.

The in F i g. The curve 21 shown in FIG. 4 shows the change in the frequency Fr of the signal emerging from the local oscillator 16 of the receiver 5 as a function of the time l. The changes in this frequency also have a sawtooth shape. at a rate increasing from FRO to FRS (the rise being linear), followed by a rapid return to the rate FRO and then a short time interval during which the rate remains constant and equal to the value of FRO. The period of the changes in the frequency FR is equal to the period T of the change in the frequency F. On the other hand, the frequency deviation between FRS and FRO is equal to. which exists between FS and FO.

A point 22 was indicated on curve 2. which represents a time of reception in the receiver 5. At this point in time, the transducer 6 of FIG. 5 receives the signals which arrive from the transducer 3 over several propagation paths. Because these propagation routes have different lengths. the individual or different signals received at time 22 were sent out by 3 at different times; B. at time 23 for the signal that arrives on 6 via the direct propagation path or at line point 24 for the signal that arrives at 6 after two reflections or at time 25 for a signal that arrives at 6 after more than two reflections arrive. At time 23, the carrier going out from 8 had the frequency Fl. at time 24 the frequency F2 and at time 25 the frequency F3. When the signals received by 6 pass through the analog multiplier or the mixer 13, they leave frequency beats with the frequency of the local oscillator 16 at the time 22, ie FR. appear. Accordingly, there is a frequency beat signal from Fl FR at output 13. a second frequency beat signal F2-FR and a third at frequency F3 FR. The filter 14 is centered on the beat frequency Fl -FR, for example. Thus, only the component of the signal that corresponds to the direct transmission path or route results at the output. In this way, within the system constructed according to the invention, a separation of signals that have propagated on different propagation paths was carried out.

The short period during which the frequency remains the same FO is used to send a synchronization signal via the generator 17 and the amplifier 10, this synchronization signal being received in FIG. 5 and enabling the linear change of the local oscillator 16 to be triggered.

The oscillator 8 of the transmitter 1 can be formed by a "voltage level generator", the a voltage / frequency converter is connected downstream. F i g-2 shows such a generator, the first Circuit of the oscillator 8 can be used.

The signals from the clock generator 12 are transmitted to the terminal 26 via a variable resistor 27 is connected to the negative input of an operational amplifier 28. as an analog integrated element is switched with a high time constantc. Here reaction the output to the input of 28 is via a capacitor 29. The positive input of 28 is connected to the ground. The output of amplifier 28 is via a potentiometer resistor 30 to the positive input of an operational amplifier 3! transferred as an analog summing element is used for the purpose of adding a DC voltage to the output signal of amplifier 28, to regulate the desired frequency change in the corresponding frequency band. The exit of amplifier 31 is at its negative input via a reaction or feedback resistor 32 connected. On the other hand, the negative input of 31 is connected to ground via one Resistor 33 and a voltage divider 34 connected via a resistor 35.

The sawtooth-shaped change at the output of the amplifier 28 results from a connection in Branch circuit on the capacitor 29 with connection of a field effect transistor. The clamp 26 normally lies at a potential of - 15 volts, and the integrator 28 supplies an output signal, the amplitude of which increases linearly. Will the When the clock pulse (clock pulse generator 12) is transmitted to terminal 26, it triggers a slightly positive pulse the transistor 36 off. which very quickly discharges the capacitor 29 by the output of the integrator 28 returns to its original position. The summing resistor 37 connects the slide of the variable resistor 30 to the positive input of the amplifier 31. The output signal of the "Voltage stage generator" is connected via terminal 38 to input terminal 39 of the voltage / frequency converter transfer.

According to a particular embodiment of the system constructed according to the invention, the linear Voltage change fn implemented a linear frequency change in a converter of the type of the in FIG. 5 converter shown, which has a flip-flop 40 with a downstream amplifier 41 and comprises a bistable multivibrator 42 which supplies square-wave signals at the output 43 with a frequency which is linearly variable.

The flip-flop 40 may include a capacitor built into a circuit how a power generator works, d. H. discharges and the. as soon as its tension is a predetermined one Value reached, causes the transmission of an impulse and immediately afterwards recharged will. The charging voltage of the capacitor is transmitted to the terminal 39 and assuming that the voltage from terminal 38 increases linearly, the time during which the The capacitor of the circuit 40 discharges simultaneously with the applied voltage. As a result, the wins Transmission frequency of the pulses by the circuit 40 linearly. The circuit 41 is one Amplifier with high input impedance that sends pulses with different sequences to the bistable multivibrator 42 supplies, which is formed by a correspondingly constructed flip-flop (flip-flop JK), this alternately from switch position 1 to switch position 0 or from position 0 to position 1

always changes when an impulse au! her departure got. This results in a frequency-modulated square-wave signal at the output of 42.

In the receiver 5, the local oscillator 16 can have a structure which is comparable to that of the oscillator 8, which is to be assumed. that the frequency band of this oscillator is chosen in the form. that a suitable beat frequency is set at the output of the mixer 13, the output frequency of the oscillator 16 being, for example, changing the position of the slider of the variable resistors 30 and 34 (see illustration in FIG. 2). According to the description of the "voltage level generator" according to FIG. 2 it becomes clear that each clock pulse leads the output frequency of the oscillator 8 from the maximum frequency FS to the output frequency FO (Initiulfrcqucn /). The clock pulse is also transmitted to the synchronization signal generator 17, which transmits a synchronization signal to the amplifier 10 at this point in time. With this sign: ^1. ! it is, for example, a pure frequency of the value FO. which, after being taken up in the receiver 5, is screened out by the filter 18, which is followed by a logic rectifier circuit 19. which in turn transmits a pulse to the oscillator 16 in the same form as the clock generator 12 sends a pulse to the oscillator 8 in order to trigger the linear change.

In the embodiment shown in FIG. 1, it was assumed that the Information was transmitted to terminal 2, which is connected to an analog-to-digital converter II. the output of which is transmitted to the modulator 9 and its operation to the control of the clock generator 12 is due. In this case of pulse modulation, the modulator 9 can be a simple analog gates act that the source suction Transmittan /. of a field effect transistor uses the carrier wave emitted by the circuit 8 to separate.

The in F i g. The receiver 5 shown in FIG. 1 is shown in FIG. 6th shown in more detail. This includes a first band filter 44 that receives the signals from the converter 6 via the terminal 45 receives and that causes a limitation of the noise band with respect to the frequencies used. This one is an analog multiplier 46 connected downstream, the other input with the output of the with variable frequency operating local oscillator 47 is connected. The output of the multiplier 46 is transmitted to a filter 48, the bandwidth of which is regulated in the form. that only a Schwcbunizssignal is transmitted, which corresponds to a single propagation distance. The output of filter 48 is transmitted with a frequency converter 49, whose second input is connected to a local oscillator 50 operating at a fixed frequency. To this In an even simpler way, the beat frequency of an interference transmission path can be filtered out will. A detection circuit is connected downstream of the output of the frequency converter 49. being it within a preferred embodiment of the transmission system * constructed according to the invention a square detector 51 acts, which in turn is a pig farm for the selection of Switching commands 52 is connected downstream. The received

Information signals are sent via terminal 53 Transfer processing sound.

Oer working with variable frequency Oits- (is / illator 47 is synchronized by the circuit 54, which the received Synchronisicrimgssignale over 44 separates. Is the shuttering 54 with a Zcitstaffelungs- or isolating circuit for the synchronization signals received from 44, originating from propagation paths of different lengths, this can use the separate synchronization signals on several exits, of which exit 55 was represented. Of the Output 55 is now connected to a second local oscillator operating at a variable frequency, which is comparable to the oscillator 47 and a signal with a variable frequency to a second Multipliers of the type 46 transmits and that in turn is a chain of like circuits in the ArI of 48, 49, 51 and 52 is connected downstream. in the Compared to that in FIG. 4 would have shown the change in the output sequence of the curve 21 Second local oscillator operating at a variable frequency, viewed as a function of time, the position of curve 56. The signal received at the time corresponding to point 57 and the same ordinate as that Point 22 of 21 and its beat frequency / is equal to Fl / - 'R. corresponds to the signal, which is transmitted in FIG. 1 at time 23 and which has followed the second propagation path. From this is thus it can be seen that with a filter like 48 at the output of the second multiplier the Signals of the second propagation path can be filtered out.

The synchronization signal generated by the generator 17 can represent a signal with a pure frequency, also a signal with pulse compression on reception, a randomly coded signal or in general any conventional sync signal.

As already mentioned, the Transmitter 1 to provide several oscillators 8, the frequencies of which are subject to parallel changes where the separation between any minimum frequency of change is sufficient to avoid any To allow interference to occur. The receiver 5 is of course with the same number of receiving channels Equipped as oscillators 8. An arrangement selected in this way enables one Parallel transmission of information on every transmission channel and in particular of digital information, each of which corresponds to a channel.

In the example described above, it was assumed that the carrier was impulse modulated, however, the system constructed according to the invention is not restricted to this type of modulation.

Analog amplitude modulation can thus be used in the same way. Furthermore the system is not limited to amplitude modulation, but is suitable for any type of Angle modulation and especially for phase modulation based on two switching states. Independent of the modulation used in each case, the bandwidth of the modulated carrier must be below remain a certain limit, that of the distances between the lengths of adjacent stretches of expansion depends.

For this purpose 2 sheets of drawings

409541/90

Claims (5)

Patent claims: 1. Procedure for the transmission of underwater signals by means of ultrasound, the carrier frequency of a transmitter and the first spatial frequency of a recipient is subject to periodic changes in accordance with a given amendment law are, characterized in that the intermediate frequency of the vibrations received to modulated carrier frequency and the first spatial frequency in the receiver through a band filter whose center frequency depends on the length of an underwater transmission link is chosen between the transmitter and the receiver and also as a function of the phase shift that is between the Change in the carrier frequency and that of the spatial frequency occurs. 2. The method according to claim 1, characterized in that the periodic change is a follows a linear law of change between a lower and an upper limit. 3. The method according to any one of claims 1 or 2, characterized in that the signal with the Intermediate frequency of a second frequency converter circuit is transmitted, which is a local signal is supplied with a second, fixed spatial frequency, the output signal of the second Frequency converter circuit see a square Detector (51) is fed to the frequency deviations of the received signals double that originate from the individual underwater propagation stretches. 4. The method of claim 3, wherein each elementary period of change of the carrier frequency of the transmitter follows after the transmission of a synchronization signal, which after rectification in a receiver of the transmission system initiating the change in the first spatial frequency causes, characterized in that this? System includes several receivers, their intermediate frequencies correspond to the same number of underwater propagation stretches of different lengths and changes in the first spatial frequencies thereof as a result of the succession of received signals triggered by the same number of underwater expansion ranges of different lengths can be received, the receiver practically in one Funct are grouped and the output signals of the square detector after passing into the Delay lines are combined, their delay values depend on the deviations in the lengths of the propagation paths. 5. The method according to any one of claims 1 to 3, characterized in that the carrier frequency composed of several sub-carriers, the several periodic changes more synchronously Art are subject to and whose laws of change are in accordance with the recipient designed for the same number of intermediate frequencies as there are subcarriers to the digital information in parallel with the same number of state pairs as auxiliary carriers transfer. The invention relates to a method of transmission of underwater signals using ultrasound, the carrier frequency of a transmitter and the first Spatial frequency of a receiver periodic changes according to a given change law are subject. When there is a connection between one above the surface of the sea and one below the surface of the sea lying point or between two points lying below the sea surface are due to Reflections on the bottom and on the surface of the water, a number of propagation or connecting routes possible. This can result in undesirable Interferences arise. In order to switch this off, converters with a very strong directional effect have already been used, which act on the Direction of the shortest or direct transmission path are aligned. This Vfcth.'de is however only possible if the sending and receiving locations are known. It is also known to encode each elementary information item during the transmission upon receipt, a comparison of each received coded elementary information with each of the elementary information the code of which is known. in order to ensure that only the information that has the best correlation is evaluated. This method requires however, an extension of the receiver with relatively complicated logical data processing devices. and it does not yet allow the separation of signals that have passed through different transmission paths. Furthermore, a method for measuring the altitude of an aircraft is known, in which the frequency a shortwave transmitter is varied between two predetermined limits. The ones reflected on the ground Waves arrive with a certain delay compared to the directly arriving waves Receiver, this deceleration value being proportional to the altitude of the aircraft above ground. the The resulting beat frequency is measured with a frequency meter and on a Measuring device displayed. In contrast, the invention is based on the object of developing the method mentioned at the outset in such a way that that interferences occurring during reception are eliminated and a separation and selection is made possible by signals that have passed through different transmission paths. According to the invention this is achieved in that the beat intermediate frequency of the received modulated carrier frequency and the first spatial frequency in the receiver through a band filter whose center frequency depends on the length of an underwater transmission link chosen between the transmitter and receiver and also as a function of the phase shift that occurs between the change in the carrier frequency and that in the spatial frequency. Exemplary embodiments of the invention are explained below with reference to the drawing, in the F i g. 1 illustrates, in block diagram form, a transmitter and a receiver made according to the invention Work system, F i g. FIG. 2 illustrates a special generator used in the FIG. 1 is used,